S. Bachmann, H. Drtick, H. Mtiller-Steinhagen

University of Stuttgart, Institute for Thermodynamics and Thermal Engineering (ITW) Pfaffenwaldring 6, 70550 Stuttgart, Germany Tel.: +49 711 / 685-63553, Fax: +49 711 / 685-63503

Corresponding Author, email: bachmann@itw. uni-stuttgart. de

Abstract

Two solar combisystem concepts have been investigated where a compression heat pump is used as the only auxiliary heater. The investigations have shown that the combination of a solar combisystem with a heat pump can result in a promising approach for saving primary energy. This especially holds true compared with a monovalent heat pump system (without a solar thermal system). However, the investigated systems show a great difference concerning the electric energy consumption of the heat pump. Especially systems where the brine is solar preheated can offer a great reduction of electric energy consumption for the heat pump.

Keywords: compression heat pump, solar combisystem, seasonal performance factor, component testing

1. Introduction

Heat pumps are presently enjoying a wide popularity in Europe. In 2007, the market for heat pumps showed a growth rate of about 100% in Germany. In recent years heat pumps were predominantly used as monovalent systems or in combination with a fossil fuel fired auxiliary heating system. At present, however, a number of new heating systems are being launched on the market where the heat pump is used as the only auxiliary heater for a solar combisystem. In addition to biomass heating systems, heat pumps offer the possibility of supporting the solar thermal system by, at least partly, renewable energy. Depending on the individual system design, there is a particular charm in combining heat pumps with solar thermal systems because this combination can provide an additional heat sink with a low temperature level so that the solar collector energy yield can be increased. For the heat pump on the other hand this approach offers a heat source with a relatively high temperature level which is beneficial for the coefficient of performance of the heat pump.

At the Research and Testing Centre for Thermal Solar Systems (TZS) in the Institute for Thermodynamics and Thermal Engineering (ITW), University of Stuttgart, two solar combisystems combined with a compression heat pump were investigated based on the component testing approach as described in the European Standard ENV 12977-2. One system consists of a compression heat pump where the condenser is located in the auxiliary section of the combistore. The other system uses an external compression heat pump in combination with an additional water store as heat source for the heat pump, which is exclusively charged by the solar collectors.

This paper presents the different system concepts. The results of the investigations such as the electric energy consumption of the heat pumps required to cover the total heat demand of the building, will be presented and discussed.

2. The investigated systems